Three related projects concerning pulmonary mass and heat transport for diffusible (gases) and poorly diffusible (aerosols) contaminants will be examined by hardware experiments and applied mathematical analysis. The overall aim is to address aspects of pulmonary transport phenomena which are motivated by physiological and clinical contexts and rooted in basic fluid mechanics. Specifically the three topics are: I. An experimental investigation of volume-cycled oscillating flow in a rigid, airway bifurcation model. In this set of experiments, a laser Doppler anemometer probe consisting of four laser beams will be directed into the oscillating flow at several grid points of selected cross sections in such a way that the local velocity may be resolved into its three dimensional structure at specific times in the cycle. Utilizing this technique will enhance our understanding of the role of axial convection, secondary swirl flows, boundary layer development and steady streaming in conventional and high-frequency ventilation (HFV). In addition, both steady and unsteady pressure measurements will be made to characterize the non-linear impedance with respect to details of the flow behavior such as vortex shedding, turbulence and streaming. II. A theoretical investigation of volume-cycled oscillating flow and mass transport in a flexible channel. A mathematical analysis of cycled flow contained by flexible walls will be carried out in order to determine the effect of tube compliance and wall motion on the fluid velocity field and, subsequently, on the predictions of net axial transports of dissolved species. We seek the dependence of Deff on Pe, alpha, A, and the dimensionless tube compliance. This analysis will assist in developing an understanding of both transport mechanisms and of oscillatory flow and impedance characteristics of normal airways and airways with altered compliance. III. An experimental investigation of volume-cycled oscillating flow in a flexible channel. By modifying the channel apparatus used in our previous experiments, we will study the deformation of dye streaks subjected to this flow regime. The steady streaming induced by flexibility will be measured using our previous techniques and compared to the predicted streaming velocities in II. Since the streaming reflects the characteristics of the unsteady velocities, it provides a check on the predicted unsteady velocity field which is of primary importance in dispersion.